Is it possible to make the variable inside nested for loop local

Is it possible to make the variable inside nested for loop local.

Yes, but only using a function.

As the builtin local can only exist inside a function, we need to provide a function to make the variable i change the scope from global to local:

#!/bin/bash

internalfunction () {
    local i     ### Works as is inside a function
    for i in 1 2 3; do
        echo "inner loop ----- $i"
        (( i++ ))
    done
}

for i in  1 2 3 4; do
    echo $i
    internalfunction
done

---

$ ./script.sh
1
inner loop ----- 1
inner loop ----- 2
inner loop ----- 3
2
inner loop ----- 1
inner loop ----- 2
inner loop ----- 3
3
inner loop ----- 1
inner loop ----- 2
inner loop ----- 3
4
inner loop ----- 1
inner loop ----- 2
inner loop ----- 3

If you run the inner variable in a sub shell, it will not affect the outer variable:

for i in 1 2 3 4; do
    (
        for i in 1 2 3; do
            echo "inner loop ----- $i"
            (( i++ ))
        done
    )
    echo $i
done

Which results in:

inner loop ----- 1
inner loop ----- 2
inner loop ----- 3
1
inner loop ----- 1
inner loop ----- 2
inner loop ----- 3
2
inner loop ----- 1
inner loop ----- 2
inner loop ----- 3
3
inner loop ----- 1
inner loop ----- 2
inner loop ----- 3
4